The present invention relates to an improvement of an optical disk apparatus.
A conventional optical disk apparatus shown in FIG. 1 is known wherein a light beam, for example, LASER 5 from an optical head 1 irradiates an optical disk 3 to form pits therein, thereby recording signals. In order to record signals in the optical disk 3 rotating at a constant angular velocity by using the above-mentioned conventional optical disk apparatus, the light beam 5, having a predetermined intensity in accordance with a distance r from the center of the optical disk 3, irradiates the optical disk 3 as shown in FIG. 2. In FIG. 2 reference symbol rO denotes the innermost pregroove. When the optical head 1 is inclined by an angle .theta. (corresponding to the incidence angle of the light beam 5 on the optical disk 3) relative to the direction normal to the optical disk 3 during radiation of the light beam 5 onto the optical disk 3, the spot of the light beam 5 to be formed on the optical disk 3 is disturbed (i.e., proper focusing cannot be performed) due to a coma. The relative inclination .theta. between the optical head 1 and the optical disk 3 may be caused by an inclination, warp or vibration of the optical disk 3. When the relative inclination .theta. is zero, the intensity distribution of the spot of the light beam 5 on the optical disk 3 is given by a curve in FIG. 3(a). However, when the relative inclination .theta. is present, the intensity at the center of the spot of the light beam 5 is decreased, as indicated by a curve in FIG. 3(b). In addition of this disadvantage, the right-hand intensity distribution becomes asymmetrical with the left-hand one, and becomes broad. As a result, when the relative inclination .theta. is present, length L of pits formed in the optical disk 3 becomes shorter than a proper length LO as shown in FIG. 4. Furthermore, when the relative inclination .theta. increases, the intensity of the spot of the light beam 5 on the optical disk 3 becomes smaller than an intensity PO (threshold power PO). The threshold power PO indicates a minimum power of the light beam 5 when a signal is recorded in the optical disk 3 (i.e., when a pit is formed). When the relative inclination .theta. is large, the signal cannot be recorded in the optical disk 3 (i.e., pits cannot be formed). In addition, as described above, when the relative inclination .theta. is present, the intensity distribution of the spot of the light beam 5 on the optical disk 3 becomes broad, as shown in FIG. 3(b). For this reason, as shown in FIG. 5, the jitter J of the signal to be recorded increases. In the conventional optical disk apparatus, when a signal recorded with the relative inclination .theta. is reproduced, the error rate of the reproduced signal is increased, resulting in inconvenience.